matthewgapp commented on code in PR #8839:
URL: https://github.com/apache/arrow-datafusion/pull/8839#discussion_r1458161958
##########
datafusion/sql/src/query.rs:
##########
@@ -65,16 +65,128 @@ impl<'a, S: ContextProvider> SqlToRel<'a, S> {
"WITH query name {cte_name:?} specified more than once"
)));
}
- // create logical plan & pass backreferencing CTEs
- // CTE expr don't need extend outer_query_schema
- let logical_plan =
- self.query_to_plan(*cte.query, &mut
planner_context.clone())?;
+ let cte_query = cte.query;
+
+ if is_recursive {
+ if !self
+ .context_provider
+ .options()
+ .execution
+ .enable_recursive_ctes
+ {
+ return not_impl_err!("Recursive CTEs are not enabled");
+ }
+
+ match *cte_query.body {
+ SetExpr::SetOperation {
+ op: SetOperator::Union,
+ left,
+ right,
+ set_quantifier,
+ } => {
+ let distinct = set_quantifier !=
SetQuantifier::All;
+
+ // Each recursive CTE consists from two parts in
the logical plan:
+ // 1. A static term (the left hand side on the
SQL, where the
+ // referencing to the same
CTE is not allowed)
+ //
+ // 2. A recursive term (the right hand side, and
the recursive
+ // part)
+
+ // Since static term does not have any specific
properties, it can
+ // be compiled as if it was a regular expression.
This will
+ // allow us to infer the schema to be used in the
recursive term.
+
+ // ---------- Step 1: Compile the static term
------------------
+ let static_plan = self
+ .set_expr_to_plan(*left, &mut
planner_context.clone())?;
+
+ // Since the recursive CTEs include a component
that references a
+ // table with its name, like the example below:
+ //
+ // WITH RECURSIVE values(n) AS (
+ // SELECT 1 as n -- static term
+ // UNION ALL
+ // SELECT n + 1
+ // FROM values -- self reference
+ // WHERE n < 100
+ // )
+ //
+ // We need a temporary 'relation' to be referenced
and used. PostgreSQL
+ // calls this a 'working table', but it is
entirely an implementation
+ // detail and a 'real' table with that name might
not even exist (as
+ // in the case of DataFusion).
+ //
+ // Since we can't simply register a table during
planning stage (it is
+ // an execution problem), we'll use a relation
object that preserves the
+ // schema of the input perfectly and also knows
which recursive CTE it is
+ // bound to.
- // Each `WITH` block can change the column names in the last
- // projection (e.g. "WITH table(t1, t2) AS SELECT 1, 2").
- let logical_plan = self.apply_table_alias(logical_plan,
cte.alias)?;
+ // ---------- Step 2: Create a temporary relation
------------------
+ // Step 2.1: Create a table source for the
temporary relation
+ let work_table_source =
+ self.context_provider.create_cte_work_table(
+ &cte_name,
+
Arc::new(Schema::from(static_plan.schema().as_ref())),
+ )?;
- planner_context.insert_cte(cte_name, logical_plan);
+ // Step 2.2: Create a temporary relation logical
plan that will be used
+ // as the input to the recursive term
+ let work_table_plan = LogicalPlanBuilder::scan(
+ cte_name.to_string(),
+ work_table_source,
+ None,
+ )?
+ .build()?;
+
+ let name = cte_name.clone();
+
+ // Step 2.3: Register the temporary relation in
the planning context
+ // For all the self references in the variadic
term, we'll replace it
+ // with the temporary relation we created above by
temporarily registering
+ // it as a CTE. This temporary relation in the
planning context will be
+ // replaced by the actual CTE plan once we're done
with the planning.
+ planner_context.insert_cte(cte_name.clone(),
work_table_plan);
+
+ // ---------- Step 3: Compile the recursive term
------------------
+ // this uses the named_relation we inserted above
to resolve the
+ // relation. This ensures that the recursive term
uses the named relation logical plan
+ // and thus the 'continuance' physical plan as its
input and source
+ let recursive_plan = self
+ .set_expr_to_plan(*right, &mut
planner_context.clone())?;
+
+ // ---------- Step 4: Create the final plan
------------------
+ // Step 4.1: Compile the final plan
+ let logical_plan =
LogicalPlanBuilder::from(static_plan)
+ .to_recursive_query(name, recursive_plan,
distinct)?
+ .build()?;
+
+ let final_plan =
+ self.apply_table_alias(logical_plan,
cte.alias)?;
+
+ // Step 4.2: Remove the temporary relation from
the planning context and replace it
+ // with the final plan.
+ planner_context.insert_cte(cte_name.clone(),
final_plan);
+ }
+ _ => {
+ return Err(DataFusionError::SQL(
+ ParserError("Invalid recursive
CTE".to_string()),
Review Comment:
done
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